The overall object of this project is to understand the mechanism of genome expression in eukaryotic organisms. Whereas much emphasis has been placed on the role of chromatin proteins in controlling gene expression, very little is known about the role of DNA modification, in this process. We intend to study DNA methylation in order to elucidate its biological role. Our research will concentrate on two main areas. We will analyze the quantitative and qualitative pattern of in vivo methylation and its relation to differentiation. For this study the developmental program of Drosophila will be utilized. We will study the relationship of methylation to chromatin structure. Since chromatin structure is the determinant of chromatin function, this will help elucidate the biological role of methylation. Finally we will test directly whether DNA methylation is involved with transcription or transcriptional control.